LT3029 LINER [Linear Technology], LT3029 Datasheet - Page 13

• Manufacturer Part Number: LT3029
• Description: Dual 500mA/500mA Low Dropout, Low Noise, Micropower Linear Regulator
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
Bypass Capacitance and Low Noise Performance
Using a bypass capacitor connected between a channel’s
BYP pin and its corresponding OUT pin signifi cantly low-
ers LT3029 output voltage noise, but is not required in
all applications. Linear Technology recommends a good
quality low leakage capacitor. This capacitor bypasses
the regulator’s reference, providing a low frequency noise
pole. A 10nF bypass capacitor introduces a noise pole that
decreases output voltage noise to as low as 20μV
Using a bypass capacitor provides the added benefi t of
improving transient response. With no bypass capacitor,
and a 10μF output capacitor, a 100mA to 500mA load step
settles to within 1% of its fi nal value in approximately
100μs. With the addition of a 10nF bypass capacitor and
evaluating the same load step, output voltage excursion
stays within 1% (see Transient Response in the Typical
Performance Characteristics section). Using a bypass
capacitor makes regulator start-up time proportional to
the value of the bypass capacitor. For example, a 10nF
bypass capacitor and 10μF output capacitor slow start-up
time to 15ms.
Figure 2. Ceramic Capacitor DC Bias Characteristics
–100
–20
–40
–60
–80
20
0
0
2
4
DC BIAS VOLTAGE (V)
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
6
8
Y5V
X5R
10
12
14
3029 F02
16
RMS
.
Output Capacitance and Transient Response
The LT3029 design is stable with a wide range of output
capacitors. The ESR of the output capacitor affects stabil-
ity, most notably with small capacitors. Linear Technology
recommends a minimum output capacitor of 3.3μF with
an ESR of 3Ω, or less, to prevent oscillations. The LT3029
is a micropower device, and output transient response is
a function of output capacitance. Larger values of output
capacitance decrease the peak deviations and provide
improved transient response for larger load current
changes.
Ceramic capacitors require extra consideration. Manufac-
turers make ceramic capacitors with a variety of dielectrics,
each with different behavior across temperature and
applied voltage. The most common dielectrics specify
the EIA temperature characteristic codes of Z5U, Y5V,
X5R and X7R. Z5U and Y5V dielectrics provide high C-V
products in a small package at low cost, but exhibit strong
voltage and temperature coeffi cients, as shown in Figures
2 and 3. When used with a 5V regulator, a 16V 10μF Y5V
capacitor can exhibit an effective value as low as 1μF to
Figure 3. Ceramic Capacitor Temperature Characteristics
–100
–20
–40
–60
–80
40
20
0
–50
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10μF
–25
0
TEMPERATURE (°C)
25
50
Y5V
75
X5R
100
3029 F03
125
LT3029
13
3029f